1. Field of the Invention
This invention relates to improvements in plating processes and equipment, and more particularly to improvements in methods and apparatuses for monitoring performance of plating apparatuses, particularly for use in plating palladium onto integrated circuit leadframes.
2. Relevant Background
Leadframes are electrically conducting structures that are used in the manufacture of packaged integrated circuit devices. Typically, a semiconductor chip is mounted onto or adjacent a leadframe, which includes a number of leads or conductors by which connections can be made to other circuitry, and the circuits of the chip are selectively connected to the leads. After the chip and leads are connected, a portion of the leadframe and the chip are encapsulated to form a package, usually of plastic, in which the chip is delivered and used.
In the construction of many leadframes, the leadframe may be coated with palladium to provide desired conductivity and other properties, and to facilitate the bonding of gold connection wires between the leadframe and the chip. The layer of palladium is a usually of importance to customers because the palladium plays an important part in enabling proper bonding of the gold wires that connect the chip to the leadframe and of enabling solid connections to be made to the leads of the leadframe in use.
However, in order to provide the desired palladium coating, multiple underlying coats are generally required. For example, on a copper leadframe, usually four conductive coats are successively electroplated onto the leadframe structure to assure the integrity of the top palladium layer. To assure that the palladium "sticks" and has the proper electrical characteristics, typically, the layer immediately below the palladium layer is nickel.
In most manufacturing processes, which are usually under computer control, however, failures in the computer system may go undetected for some time. This may result in production of potentially large lots of unacceptable leadframes. It may be, in fact, possible for defective product to be shipped to the customer, resulting in the subsequent production of parts which may not meet specifications and which may require expensive identification, correction, and substitution of proper parts.
To address these problems, frequently the production lines have been monitored by x-ray equipment, in which the thickness of the material being deposited is x-rayed. Such x-ray monitoring, however, requires manual operation, and also requires expensive equipment, which itself requires expensive regulation and maintenance.
What is needed, therefore, is a method and apparatus for monitoring the electroplating process so that if the conditions required for proper palladium electroplating become improper to form the desired palladium layer, an operator can be warned, or, optionally, the production line can be automatically shut down.